GB847770A - Improvements in the purification of dimethylformamide - Google Patents

Abstract

Dimethylformamide which has been used in the dry spinning of polyacrylonitrile and which has had its water content reduced to 0,25% or less is further purified so as to be suitable for re-use in the dry spinning by contacting it with a strong acid cation-exchange resin and a weak base anion-exchange resin, both resins having been colour-conditioned by contact with dimethylformamide until they no longer lose colour to the dimethylformamide. The resins may be used in separate layers or beds, the cationexchange resin then being preferably used first, or in mixed beds. Suitable cation-exchange resins are sulphonated phenollformaldehyde and sulphonated polysterene/formaldehyde resins, e.g. having an apparent acidity of pH 3-5 ; and suitable anion-exchange resins are of the nonquaternary polyamine. type, e.g. having an apparent basicity of pH 8-11. The regeneration of the resins is described.ALSO:Substantially anhydrous impure dimethylformamide is purified by contacting it with a strong acid cation-exchange resin and a weak base anion-exchange resin until it is substantially free from coloured and colour-forming impurities, both resins having previously been colourconditioned by contact with dimethylformamide until they no longer lose coloured constituents to the dimethylformamide. The resins may be used in separate layers or beds, the cation-exchange resin then being preferably used first, or in mixed beds. Suitable cation-exchange resins are sulphonated phenol/formaldehyde and sulphonated polystyrene/divinylbenzene resins, e.g., having an apparent acidity of pH 3-5, ; and suitable anion-exchange resins are of the nonquaternary polyamine type, e.g., having an apparent basicity of pH 8-11. The regeneration of the resins is described. A suitable dimethylformamide feed comprises dimethylformamide recovered from the dry spinning of polyacrylonitrile. Specifications 472,404 and 595,043 are referred to.